Humidity control for refrigerated spaces



March 7, 1939. w. H COOK 2,149,990

HUMIDITY CONTROL FOR REFRIGERATED SPACES Filed Nov. 22, 1937 2Sheets-Sheet l mm vm ooooooo o ooooooo \woaooooo w. H COOK 2,149,990

Filed Nov. 22, 1937 2 Sheets-Sheet 2 Fig.5

HUMIDITY CONTROL FOR REFRIGERATED SPACES March 7, 1939.

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Patented Mar. 7, 1939 I HUMIDITY 'coN'moL F 11. REFR'IGERATED' smosWilliam Harrison Cook, Ottawa, Ontario, Canada Application November 22,1937, Serial No. 175,852

12 Claims.

This invention relates to a method and means for maintaining andcontrolling humidities of the atmosphere in refrigerated storagecompartments.

An object of the invention is to provide a method and means 'formaintaining and controlling the humidity in refrigerated spaces with thevminimum addition of heat to the refrigeration load.

A further object is to increase the efllciency of heat transfer fromsurfaces of the cooling elements to the atmosphere in refrigeratedspaces by maintaining these surfaces free from ice by means of liquidflowing over them. The prevention of ice formation on the coolingsurfaces also avoids the addition of the-latent heat of fusion of suchice to the refrigeration load. Broadly the invention consists inspraying a suitable liquid over the cooling elements to prevent moisturefreezing thereon and to collect condensed moisture, collecting thisliquid for recirculation, and causing a portion of the liquid to beboiled in an insulated heater to provide watervapor which is dischargedinto the refrigerated space when high humidities are desired, or whichis exhausted externally of the refrigerated space when lower humiditiesare desired.

The invention will be described with reference to the accompanyingdrawings, which are more or less diagrammatic and in which,

Figure 1 is a sectional view of an apparatus embodying the invention asapplied to a cold storage space,

Figure 2 is an end sectional view of the apparatus, the intervening wallof the storage space being omitted,

Figure 3 is a partial end sectional view of a modified form ofapparatus,

Figure 4 is a side sectional view of another 4 form of heaterarrangement and Figure 5 is an, end sectional view of the arrangementshown in Figure 4.

In the drawings, I" is the refrigerated space having insulated walls 2,and 3 the cooling coils, 45 containing a refrigerant, preferablypositioned in the upper portion of thespace.

Means for preventing ice formation on the cooling coils as a result of.freezing of condensed moisture thereon comprise a spray pipe 4 locatedabove the coils in a position to spray the same, a pipe 5 for supplyingspraying liquid thereto, a tank 6 containing a suitable liquid, and apump 1 with motor 8 for circulating the liquid through the pipe. A valve9 and a screen III for the liquid may be provided adjacent'the inlet ofpipe 5. A

pressure release for the liquid in pipe 5 consists of a pipe ll leadinginto the tank provided with a relief valve l2.

The liquid employed must be capable of dissolving, ice at thetemperature of the cooling surfaces of the refrigeration coils, and alsoof yielding only an aqueous vapor when heated. Brines, for instance,calcium chloride, are suitable, as are also solutions of ethyleneglycol. Qbviously' the liquid used will have a lower vapor pressure 1than that of ice at the temperature of the refrigeratingsurfaces and thevapor pressure, which varies with concentration of the liquid, makesdehumidification possible when the aqueous vapor is exhaustedexternally. V

Means for collecting'the sprayed liquid and returning it to the tankcomprise drip pans l3, insulated'on the under side where necessary andlocated below the coils, louvers II at the side of the coils fordirecting the liquid into the pans 2 and a return pipe l5 leading fromthe pans to the tank. A space I6 is provided between the pans to ensurenecessary air circulation around the coils, baiiles I1 being providedabove the space to direct the sprayed liquid into the pans. A tankoverflow pipe l8 may be provided.

Means for maintaining a suitable humidity in the refrigerated spacecomprises a heater l9 "preferably positioned outside the space, as shownin .Figure 1, and having an electrical heating element within a casing2| surrounded with insulation 22. Liquid is supplied to the heater bymeans of a pipe 23 having a valve, a return pipe 25 having a valve 26being provided for the liquid. Water vapor formed in the heater risesthrough an insulated channel 21 for escape through an outlet ,28 to therefrigerated space when a higher humidity is required therein or, bymeans of a flap .valve 29, through an outlet 30 to the exterior of thespace when a lower hu- I 40 midity is required. In largerefrigeratedspaces, itmay be necessary to provide a distributing fan forthe vapor at the outlet 28.

- A circulation of the liquid through the heater and back to the tankmust be provided to prevent accumulation of the non-aqueous portion inthe heater. Since the concentration of the liquid with respect to thenon-aqueous phase must be changed to accord with the temperature of thecooling surfaces, the rate of circulation should be varied accordingly.For instance a highly concentrated solution necessitates a greatervolume of liquid in circulation through the heater than with dilutesolutions if accumulations of the.non-,

aqueous portion therein are to be avoided. Ac-

. cording to the invention the circulation between the heater and thetank is preferably restricted to .the minimum neediul tor the operationso that the minimum. amount of sensible heat is added to the tank. It isobvious that the sensible heataddedtothetankisaddeddireotlytothereirlg-'-eratingloadwhi'chispreferablykeptaslowas possible.

The restriction andcontrolor the circulation areaccolnplished by aparticular arrangementoi thetank and heater without strlctlons in thepipe line. The tank is divided intoan upper or auxiliary iliarycompartment, and the return pipe. 28, which communicates with astandpipe 34 through a heat exchanger Si in the heater, empties into'the main compartment. The return pipe il from upward through. a verticalportion or pipe ll, to

the drip empties into. the auxiliary, oompartment and the level orliquid therein is controlled by means of an adjustablestandpipellleading from the auxiliary to the main compartment. Theheater is so positioned-adjacent the tank that it willbe ted byigravitywith liquid from the auxiliary compartment ii, the inlet pipe 2]communicating-with the bottom oi the heater casing 2i. It ,will beobserved that the inlet or standpipe N is the inlet to pipe 23 in thecompartment SI and at substantially the same level as the outlet oi pipell. A head or liquid is thus provided to control the flow or the portionoi liquid to be circulated through theheater.Therateoiiiowthroughtheheater is determined bythe difl'erence inflevelbetween the standpipe II and the level in the auxiliary compartl'nentSh-which latter level is regulatable by the adjustable standpipe a. Inorder to conveniently odate the heater adjacent th'tank, it may beinclined somewhat as shown inl 'lgure 2.' I

. The stand pipe 34 in-the heater communicates with return pipe IIthrough the heat exchanger. )5. v When the apparatus is in operationliquid 'ilows down the heat exchanger, 'where as much as possible of theheat is removed,- then prevent air locks, and finally discharges intothe main compartment of the tank 8!, ate. level substantially the sameas that of the heater standpipe. as. Valves H, in the supply pipe 28,and it, in return pipe II, are provided for servicing:

"'mater'ialintheheaterw- Means are provided for automatically discon-'or for the ilow temporarily in an emergency. The liquid entering thesupply pipe ll ir'on the auxiliary compartment ll is preierably screenedas at- It to prevent choking oi the lines and undesirable accumulationsof insoluble necting ,theheater from its heating circuit when for anyreason the circulation oi liquid in the spraying system, is" stopped, asfor. instance, through failure oi the pump. Asillustrated, this meanscomprisu a small unrestricted opening Il leading i'romthe auxiliarycompartment to the main compartment --of the tank through which theliquid in the. auxiliary compartment may drain and afloat ll connectedto actuate a switch a in the heating circuit 40' when the liquidlevelcaches the bottom or the auxiliary compartshown diagrammatically inFigure 2. 8 illustrates an alternativearrangement .9m ment, as Figure Ior the inlet and outlet'pipes oi the heater. As

shown, the liquid isdelivered firstly to the heat euchangerIlbyaninletpipell andthentothe II and a lower or main compartment 82; Asshown, the inlet pipe 23 for the heater leads iron the aux-1 heaterthrough standpipe u. the return flow uring place through a standpipe. 42 communicating with the base of the heater. In this arrangethe heateris controlled as previously described by adjusting the standpipe 33 togive the desired level in the auxiliary compartment II. In this 'mentthe restriction oi the rate or flow through arrangement the outlet leveloithe heater standi e .must be below the liquid level in the heater asfixed by the outlet level of the return standpipe 12, and this latterlevel is below thstilned by adiustable standpipe 33.

Figures 4 and 5 illustrate another embodiment of the heater arrangement,the spraying system being the same as that previously'described. As

' shown, the tank 6 comprises but a single compartment, a minimum level0! liquid as indicated at, being maintained therein. A heater ll,

closely similar to heater l9, comprises a casing 46 with'an insulatedcovering 46, a heating element 41, a water vapor channel-48, vaporoutlet49 to reifrigera'ted space and vapor-outlet 50 to exterior ot thespace-controlled by avalve II.

The heater ll may be mounted adjacent the tank within the refrigeratedspaceand a liquid inlet 52, with valve-i3, communicates with the bottomthereof. The heater is so positioned, ,as shown.

that't'he liquid level therein will be maintained,

by gravity, at substantially'the same liquid level as the tank. Thisheater is also inclined with respect to the tank for convenience-oiarrangement.- A return pipe 54 with a valve 55 for the liquid isprovidedv just slightly below the level of liquid in the tank andheater. The retu'rn pipev 54 is provided with u restricted passage it ofsuch a sizethat the circulation of liquid through the heater isadequatefor preventing troublesome concentration or the non-aqueous part oi! theliquid in: the heater and is preferably restricted so .that a minimumamount of sensible heat is added to the tank. "The valve Il may also beused for controlling the circulation. r I

The liquid inlet 5.2 may be provided with a screen 51.

While the heater .is shown outside the refrigerated space .in. theembodiment of Figure 1 and within the space in the embodiment of Figure4, it will be readily understood that the position 01' the heater isentirely dependent upon the par I 'ticuiar installation being made. I!placed within the space,'th e necessity oi. heavy insulation there-. foris more important.

required at low temperature, 1. e., or the order oi 0' I". or lower.Under these conditions, the eir culatingmedium must be quiteconcentratedto prevent theiormation or ice, and this requires thecirculation of a relatively large-volume oi the medium in relation tothe amount of water evaporated; There being no restricted passages inthe shown in Figures 1 and 2 is v letter embodiment, choking of thelines by 'crys-J tallization oi the non-aqueous portion 01' the liquidisavoided; even when a concentrated brine I solution is employed. Theembodiment shown in 'Figures 1 and 2 also requires less liquid tomaintain the'minii'n'um levels necessary'in operation.

This is important it expensive liquid such as ethylene glycol is used.'1

The humidity in the refrigerated W may be controlled either manually orautomatically by controlling the heat input to the heater. Most of thepresent commercial devices used for the automatic control of relativehumidity are slow in response and comparatively insensitive at tained ina closed space below the freezing point with constancy with practicallyno adjustment of Fluctuations in the outside temthe apparatus. peratureand other changes affecting the amount of heat to be eliminated from thespace cause slight, but generally insignificant, fluctuations in therelative humidity. Where the space is not closed but subject to periodicopening of doors and the like, a loss or gain in the total moisturecontent will occur, with consequent slight changes in the concentration.of the aqueous medium in the tank. The concentration of the liquidmedium may be adjusted periodically, for instance, by exhausting watervapor formed;by the heater outside the refrigerated space or by addingwater or the non-aqueous phase as required.

It will be observed that the heat required for humidification is reducedto a minimum by arranging to have the highest possible proportion of theheat supplied as latent heat in the form of water vapor, instead of assensible heat..

As previously stated, the described method of and means for humiditycontrol in refrigerated spaces, is capable of maintaining and.controlling humidities in the vicinity -of saturation, which is thecondition usually required in refrigerated spaces held at temperaturesbelow the freez point of water. It is well known that most perishablefood stuffs require the surrounding refrigerated atmosphere to bekept ata relative humidity of 95% or higher in order to avoid desiccation withconsequent deterioration in quality and value. These high relativehumidities cannot be obtained by the mere addition of Water vaportorefrigerated spaces, owing to the dehydrative effect of therefrigerating surfaces, which become coated with ice, thus leading -to asecond effect previously mentioned, namely, a decreased efiiciency ofheat transfer.

In actual trials of the apparatus described, it has been found that-thehumidity was raised to over 95% and maintained at these values with theair temperature at 14 F., with the mean temperature of the refrigeratingsurfaces at 1 F. The heat transfer efliciency of these surfaces wasrelatively 50% greater with than without the humidity control described.The relative humidity in the space without the present control neverexceeded 80%, a condition which caused severe, desiccation of the storedperishable food commodities.

The method and means described are applicable wherever distribution ofbrine or other suitable liquids over cooling refrigerating, surfaces andcollection 'of the same can be arranged.

It may be noted that the invention is applicable for increasing ordecreasing the relative humidity in storage or like spaces attemperatures well above and well below the freezing point.

It will be understood that the means for carrying out the invention mayvary widely without departing from the scope thereof. Moreover,

, the water vapor such means will necessarily be altered to meet varyingconditions of installation.

I claim:

1. A method of controlling the humidity in a closed space having coolingelements which comprises applying an aqueous spray to the surfaces ofthe cooling elements to prevent moisture freezing thereon and to collectcondensed moisture, recovering the aqueous spray withitsaccumulatedmoisture, continuously vaporizing water in a portion of therecovered sprayand delivering within or without the space as required.

, ,2..,A method of controlling the humidity in a closed space havingcooling elements which comprises applying" an aqueous spray to thesurfaces of the cooling elements to prevent moisture freezing thereonand to collect condensed moisture, recovering the aqueous spray with itsaccumulated moisture, continuously circulating a portion of therecovered spray through a heater to vaporize a portion of the watertherein and delivering the vapor within or without the space asrequired.

3. Humidity control for refrigerated spaces having cooling elements witha refrigerant circulating therethrough comprising means for spraying anaqueous liquid upon the surfaces of the cooling elements, said liquidhaving a freezing point below the temperature of said surfaces, meansfor recovering the sprayed liquid, a constant level tank adapted toreceive the liquid, a heater disposed adjacent thereto and having aliquid inlet communicating therewith, said heater being adapted to boilthe liquid therein to form water vapor, a standpipe in the heateradapted to withdraw liquid from the heater, said standpipe having aninlet at a level below that of the constant level tank, and means fordelivering the vapor within or without said space.

4. Humidity control for refrigerated spaces having cooling elements witha refrigerant circulating therethrough comprising means for spraying anaqueous liquid upon the surfaces of the cooling elements, said liquidhaving a freezing point below the temperature of said surfaces, meansfor recovering the sprayed liquid, a constant level tank adapted toreceive the liquid, a main tank adapted to receive the overflow fromsaidconstant level tank, means for adjusting the level in said constantlevel tank, a heater disposed adjacent the constant level tank and having a liquid inlet communicating therewith whereby liquid is supplied tothe heater by gravity, said heater being adapted to boil the liquidtherein to form water vapor, a standpipe in the spraying an aqueousliquid upon the surfaces of the cooling elements, said liquid having afreezing point below the temperature of said surfaces, means forrecovering the sprayed *liquid, a tank adapted to receive the recoveredliquid, a heater disposed adjacent the tank and having a liquid inletleading from the tank to the lower portion thereof, said heater beingadapted, to vaporize a portion of the moisture in said liquid, a liquidoutlet leading from the upper portion of the 4 heater to metank, saidoutlet having a restricted orifice to control passage of liquid throughthe outlet, and means for delivering the vapor by the heater within orwithoutthe space.

6. Humidity control for closed'spaces having cooling elements with arefrigerant circulating therethrough which comprises means for supplyingan aqueous fluid having a freezing point" -below the temperature of thecooling element surfaces, means for spraying said fluid upon saidsurfaces, means for recovering said sprayed fluid,

means forcontinuously and reguiatably frac- I tionally dividing saidrecovered fluid, a' heater adapted and arrangedto vaporize a portion ofthe water of oneof such fractional divisions, means for delivering thewater vapor within or without said space andtmeans for returning theconcentrated fluid to,said fluid supply.

freezing point below the temperature of said surfaces, recovering theaqueous spray with its accumulated moisture, continuously vaporizing apart of the recovered spray and delivering the 'water vapor to thespace.

I 8. A method of maintaining the humidity in' a closed space havingcooling elements adapted to provide a temperature of 32 F. or lower insaid space which comprises supplying an aqueous" liquid for-continuousapplication in the form of a spray to the surfaces of the coolingelements to prevent moisture freezing thereon and to collect condensedmoisture,.said aqueous liquid hav ing a'freezing point below thetemperature of said surfaces, recovering the sprayed liquid-with itsaccumulated moisture, continuously circulating a portion of therecovered spray through a heater to vaporize a portion of the waterthere- .in, and delivering the water vapor to the space,

surfaces, recovering the sprayed liquid with itsaccumulated moisture,continuously and regulatably fractlonally dividing'said recoveredliquid, vaporizinga portion of the water of one of suchfractional-divisions delivering the water vapor formed within or withoutthe space as required andreturning the concentrated liquid totiieaqueous liquid supply.

10. Humidity 'control for refrigerated spaces having cooling elementswitharefrigerant circulating therethrough comprising means for sprayingan aqueous liquid-upon'ithe surfaces of the cooling elements, saidliquid having a freezing point below the temperature of said surfaces,means for recovering the sp yed liquid, aconstant level tank adaptedt oreceive the recovered liquid, a heater having aliquid inletcommunieating with theconstant level tank, said heater being adafp theliquid therein and to vaporize water from saidiliquid, a; liquid outletleading from theheater, means for controlling the flow of liquid throughsaid heater, and means for delivering ted to receive therefrom a portionof the vapor formed by the heater within or without said space. a

ll. Humidity control for closed spaces having cooling elements with arefrigerant circulating therethrough which comprises means forsprayingan aqueous liquid upon the surfaces of the cooling elements,said liquid having a freezing point below the temperature of saidsurfaces. means for recoveringthe sprayed liquid, a constant level tankadapted to receive the recovhaving cooling elements with a refrigerantcir- I culating therethrough comprising means for spraying an aqueousliquid upon'the surfaces of the cooling elemients to prevent moisturefreezing thereon and to collect condensed moisture, said liquid having afreezing point below the temperature of said surfaces, means forrecovering the sprayed liquid, a heater having-inlet means providing aconstant supply of said recovered liquid thereto, said heater beingadapted to vaporize a portion of the water in the liquid suppliedthereto, said heater having liquid out"- let means adapted to maintain acontinuous circulation of liquid through the'heater, means forcontrolling the rate of flow of liquid through the heater, and means fordelivering the vapor within or without'said space.

' WILLIAM HARRISON COOK.

